The incorporation of science into environmental policy is a key concern at many levels of decision making. Various institutions have sought to standardize the protection of natural resources by requiring that decisions be made based on the "best available science." Here we present empirical data describing the incorporation of best available science in the land-use policy process on a local scale. Results are based on interviews with planners and others who conducted scientific reviews associated with a Washington State Growth Management Act amendment that requires the inclusion of best available science in protecting critical areas. Our results show that jurisdictions varied with respect to how they included science in their land-use policies. Specifically, we found that smaller jurisdictions were very reliant on scientific information provided by state agencies, communicated frequently with other jurisdictions and agencies, and most often let scientific information guide the policy development process. Medium-sized jurisdictions, in contrast, were more inwardly focused, relied predominantly on local information, communicated little with outsiders, and more often looked to political influences to guide the policy process. Large jurisdictions, including most counties, often generated their own best science, communicated with and often informed state agencies and other jurisdictions, and more often considered science first during the policy development process. Jurisdictions also differed in terms of how best available science was defined, and how jurisdictions dealt with conflicting scientific information. Our results provide empirical evidence of the variation with which best available science is used in environmental policies.